This invention relates to a marine propulsion unit and an improved drive shaft arrangement therefor. More particularly, the invention relates to the upper drive shaft portion and its mounting adjacent the clutch apparatus.
As disclosed in U.S. Pat. Nos. 4,244,454, 4,257,506 and 4,630,719, the generally vertical drive shaft providing the main drive connection between the engine and lower propeller unit has conventionally been mounted at its upper end adjacent the clutching mechanism for reverse and forward drive. The clutching mechanism has included spaced forward and reverse bevel gears which are selectively engaged by a shift sleeve mounted to the drive shaft.
Heretofore, the drive shaft has been provided with a lower annular groove adjacent the forward drive bevel gear, and an upper annular groove adjacent the reverse drive bevel gear. A separate annular lower thrust collar has been positioned adjacent the lower groove, while a separate annular upper thrust collar has been positioned adjacent the upper groove. The thrust collars have been assembled to the drive shaft by sliding them onto the shaft ends, one by one, and locking the collars into position by means of arcuate keepers which have been snapped into place in the grooves.
The conventional construction has been of costly design due to the very close tolerances required between the keepers and the grooves. Furthermore, assembly of the parts has not been easy. In addition, it has been observed that the drive shaft has tended to fracture or break in the area of the lower groove.
It is an object of the present invention to substantially reduce and/or eliminate the aforementioned problems.
It has been known that the thrust forces from the engine output shaft are always transmitted to the main drive shaft at a position below the upper collar, regardless of whether the drive is operating in forward or reverse. Thus, the problem of shaft breakage in the vicinity of the lower collar and at the lower groove is believed to have been caused primarily by the reduced amount of metal available at the lower groove combined with the subjecting of the lower groove area to the thrust forces whenever the shaft is driving.
In accordance with the various aspects of the invention, a marine propulsion unit is provided wherein the main drive shaft includes an integrally formed annular portion of enlarged diameter at the location of the previously utilized lower groove and keepers. The enlarged diameter portion increases the mass and strength of the shaft at a position subject to subtantial torque forces, thus substantially eliminating problems of shaft fracture or breakage. In addition, the enlarged diameter portion is formed in the shape of a thrust collar so that the shaft can be accommodated by the previous known shaft mounting elements without redesign of the latter.